Cardiac resynchronization therapy involves pacing the left ventricle (LV) with a pacing electrode that are disposed on a pacing lead, placed within the coronary venous system. Placement of the pacing lead is severely limited by anatomical factors, especially venous anatomy. One of the most common issue is phrenic nerve pacing, a problem that can be seen in 40% of patients who undergo this procedure. The problem of phrenic nerve pacing occurs because the phrenic nerve is attached to the parietal pericardium, and the coronary vein is an epicardial structure, just beneath the pericardium. Hence, the pacing electrode can be immediately adjacent to the nerve leading to diaphragmatic pacing, and leading to patient discomfort. Some of techniques employed for phrenic nerve avoidance include one described in U.S. Application No. 20030065365 that describes detecting diaphragmatic or other skeletal muscle contraction associated with the output of a pacing pulse. Upon detection of diaphragmatic contraction, the device may be configured to automatically adjust the pacing pulse energy and/or pacing configuration. U.S. Application No. 20130046356 describes another technique using segmented electrodes. PCT/US2005/031559 describes a technique to address electrode individually, such that each may be activated individually, or in combinations with other electrodes with the aid of the multiplexing circuits on the Integrated Circuits. Some other techniques include electronic repositioning (simply choosing a different vector). As one skilled in the art would know these techniques require further electronic hardware or post-processing software and do not remove the risk of pressing the phrenic nerve.
Other factors that limit lead positioning include markedly elevated pacing thresholds at certain locations. Hence, more often than not, the lead is not placed at the desired location. Rather, the lead is placed at the site where the vessel anatomy allows placement. Besides anatomical limitations, lead positioning is also often limited by technical factors including accessibility, & lead stability within the appropriate region of the appropriate vein.
Techniques for appropriate placement of cardiac lead in the intravascular or pericardial cavitary locations such as left ventricle (LV) are continuing to be developed. Some techniques currently used include advancing the lead distally into a progressively narrowing vein until it can not be advanced any further, another technique includes a mechanism where, upon removal of the stylet, the lead assumes a predetermined S-shape, and some other techniques employ plastic lobes along with the lead that expand upon deployment in the cardiac region.
Despite these advancement, the failure rate of cardiac lead implantation still averages up to 10% in most large studies. And such issues are faced even while using the lead for stimulating other regions of the body such as specific nerves in the nervous system. Thus there is a need for improved technique and system to ensure stimulation electrodes are positioned only at region of interest.